The present invention relates to a method of fabricating nano-size thin wires with a diameter of 100 nm or under and devices having such nano-size thin wires.
A thin metallic wire of a 100 nm diameter or smaller has specific properties called quantum conduction phenomena, such as follows: (a) Phase information of conduction electrons survives and the electron wave interference effect becomes obvious. (b) Ohm's law is often broken and the electrical conductivity (and consequently thermal conductivity as well) of the wire depends on the configuration of the metal as well as its diameter and length. (c) The conductivity greatly fluctuates and noise is observed depending on the configuration of the sample and the positions of impurity atoms. (d) A marked surface effect is produced. (e) Visible light enters throughout the thin wire, causing a decrease in its conductivity.
Two methods have been proposed to fabricate nano-size thin wires. According to a first method called the IBM laboratory method, a gold (Au) evaporated film is formed on the surface of a graphite substrate, then an arbitrary thin line, along which a thin wire is desired to obtain, is drawn on the Au evaporated film by means of an electron beam, and at the same time, carbon (C), which results from the decomposition of a residual gas such as CH.sub.4, is deposited onto the thin line. After the carbon film is grown to a proper thickness, the Au evaporated film is removed by argon (At) sputtering, and at the same time, the carbon line deposited thereon is also removed. As a result, the gold underlying the carbon thus removed remains unremoved, providing a nano-size thin wire of the same shape as that of the thin line drawn by the electron beam. According to the second method by Yale University, a step line is formed by argon sputtering on the surface of a glass substrate, then a metal thin film is evaporated onto the substrate surface where the step line was formed, and argon sputtering is performed again obliquely, leaving an Au thin wire in the shade of the step line.
With the first-mentioned prior art method in which the Au evaporated film surrounding the thin carbon line and the carbon line deposited on the Au film are removed at the same time and the gold line underlying the carbon line is left unremoved, it is necessary that carbon be deposited thick, and therefore, the Au evaporated film must be scanned repeatedly by the electron beam along the thin line. This consumes much time, and hence constitutes an obstacle to mass production of thin wires and inevitably raises their manufacturing costs. The second-mentioned conventional method is defective in that the crystal growth of the thin wire is not uniform under the influence of the glass substrate and that during sputtering using argon (Ar) ions the thin wire is contaminated (with an impurity entering it) and the wire surface is roughened.
Since the conventional thin wire is formed directly on the substrate as mentioned above, it is likely to be affected physically by an interaction between the substrate and the thin wire. Moreover, there is a fear that atoms forming the substrate and/or impurity elements in the substrate enter into the thin wire to form an alloy which chemically affects the thin wire. In addition, the thin wire cannot be separated from the substrate.